The efficacy of hormone assays in the differential diagnosis of amenorrhea and menopause.

The differential diagnosis of menopause and amenorrhea is currently based on the assay of circulating follicle stimulating hormone, luteinising hormone, and estradiol. The diagnostic performance of the three hormone assays, both as single and combined tests, was evaluated considering as reference data the results from 300 subjects for either condition, and assuming menopause-amenorrhea prevalence ratios corresponding to 1 and 10. In the calculation an "allocation" scheme was adopted, and the uncertainty associated with the diagnostic performance parameters was accounted for.

The uncertainty associated with the predictive value of test results.

The uncertainty associated with predictive value of test results was taken into consideration, as concerns both sampling error (related to the size of the statistical reference samples) and analytical imprecision (unavoidably involved by the measurement itself). A software package, developed for the statistical calculations, was used for the treatment of the results obtained for serum free thyroxin in euthyroid and dysthyroid subjects, assumed as an experimental model. Examples are shown for the obtainable functions predictive value vs.

Error models and quality control performance.

As an alternative to the oversimplified error schemes currently adopted in establishing quality control (QC) strategies, a complex model was assumed implying (a) the distribution of errors (critical error is regarded as a value discriminating between "effective errors" to be detected and "subcritical errors" which do not interfere with the medical decision whose detection is considered as a false-reject signal), and (b) the possibility of simultaneous losses of precision and accuracy. The control data recorded for digoxin radioimmunoassay over a one-year period were used for (1) deriving the probability density functions of random and systematic errors, through a within-run across-level normalisation procedure; (2) obtaining the functional relationships between the critical random or systematic error and the QC performance statistics (sensitivity, specificity, predictive value), weighted for the error prevalences, through integration of the probability density functions and the power functions associated with an exemplifying control rule; and (3) describing the functions which correlate the corrected performance statistics with the allowable error (whose individual values account for all possible combinations of critical random errors and critical systematic errors), by extending to the tridimensional space the above procedures. Analysis of the resulting data shows that it is necessary to revise the criteria for the choice and optimisation of QC schemes.

Italian external quality assessment scheme in immunoassay.

This paper deals with the organization, the data processing and some of the results obtained in Italian external quality assessment (EQA) schemes for hormones, tumor markers and hepatitis B markers. The EQA for hormones and tumor markers includes up to sixteen analytes together with the participation, in 1990, of about 250 laboratories. Laboratory results were used to prepare periodic and end-of-period reports.

Performance assessment of coupled tests: the effects of statistical non-independence.

Limited to two-test associations (series and parallel schemes), the effects of statistical non-independence were studied through a mathematical approach and an experimentally-based evaluation. Both procedures were applied to results for total hormones and free fractions in euthyroid and dysthyroid subjects. Assuming independence, the sensitivity of combined tests was found to increase in parallel coupling, and to decrease, symmetrically, in series coupling, depending critically on the degree of between-test correlation and on the value of single test sensitivity (the opposite modifications obviously occur for specificity).